Grav Tanks

[BMonnery]

Hi,

I found an old message from myself in the etranger list archive. I'd been reading a 2nd hand RCEG and thought the gravtank was odd, so posted this, thoughts?

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I thought the Grav Tank in RCEG was odd, so I modified it. Any
comments?

Trepida Grav Tank
The Trepida was the standard grav tank of the 3rd Imperium and is a
fairly standard Grav Tank, capable of being built on any TL-14 world
and equipping the Imperial Marines and many Planetary Army units. The
primary weapon is a rapid fire 25mm Mass Driver Cannon, throwing a
600g Bonded Superdense Penetrator at Mach 18 (6000 mps). A close up
weapon capable of defeating the majority of grav tanks front glacis,
and every fighting vehicles weaker side and aft armour. At longer
ranges missiles are employed. Upto 10 Javelin hypersonic missiles may
be carried. These are 250kg high speed missiles capable of engaging
armour and aircraft at long ranges. Should infantry opposition be
expected then vast numbers of 70mm rockets can be carried. As a final
holdout, and providing point defence against incoming missiles are 2
VRF Gauss Machineguns.

The Grav Tank was always acted more like an old 21st century attack
helicopter rather than a conventional "tank" of that time. Grav Tanks
are usually employed in combined arms formations with the standard
Lift Infantry Battalion consisting of 3 Lift Infantry companies in
Astrin Grav IFVs and a squadron of 14 Grav Tanks. The Grav Tanks role
is counter enemy armour, strike deep into their rear and provide
close support to the Battlesuited Infantry of the Battlegroup. Most
attacks are pop-up in nature, emerging from NOE just long enough to
unleash a barrage of missiles and 25mm fire, destroying their target
before moving back down to the safe area.

Since the fall, most Grav Tanks have ceased to function, but even a
small cache of working Trepidas can provide a huge amount of power on
a world where nothing can counter it. Since TL14 MDAC rounds are
scarce, many have been replaced with more primitive autocannon.
General Data
Tech Level: 14
Price: ~ MCr2
Size: Very Small (140m3)
Mass: 65.14 T loaded (with fuel, 400 25mm, 30,000 4mm and 2.5 tons of
launched ordnance).
Engineering Data
Power: 5.37 MW Fusion Power Plant supplying power to high-efficiency
contra-grav lifters and HEPlaR thruster generating 58.65 tonnes of
thrust (0.0123 MW excess power)
Maint: 43
Engineering Data
Controls: Dynamic-Linked, TL10+ Avionics, TL14 TF avionics, 3x TL14
Flt computer, TL10+ IGS navigation.
Comunications: 3000 km radio, 2x 3km masers.
Sensor: 3km active EMS, 30km passive EMS (Surface Search), 3000km
passive EMS (Air/ Orbit Search), 2x Wide Spectrum Viewers.
ECCM: EMM, Four decoy dispensers with 20 decoys each.
Life Support: Extended Life Support, G-compensators, one airlock.
Cargo: Negligible
Crew: 2 (driver, commander/gunner)
Passengers: None.
Armament
Offensive: Turret mount with TL14 25mm Mass Driver Autocannon, and
coaxial VRF gauss gun. One cupola, with VRF gauss gun. Ordnance Bay
(2.5 tons of tactical missiles, anti-tank missiles, rockets, bombs
etc.)
Defensive: None
Ammo: 400 rounds 25mm (5.77 tons, including carts); 30,000 darts for
each VRF gauss gun.
Fire Control: EMS Rangefinder, TL14 point defence ballistic computer.
Stabilization: Advanced

Round ROF Dam val C-B Pen Val Short Rng
Ammo Price Ammo Weight
25mm APFSDSBSD SA5 6 269-269-259-249
3000m* Cr27 (plus Cr28 for cart) 600g
4mm gauss dart 50 7 2-2-2 230m Cr.01 0.5 g
* Limited to 3000m by fire control, 6,600m by energy
Movement
Speed: 800 kph maximum speed, 800 kph cruise speed, 160 kph safe NOE
speed (3,150kph in vacuum).
Travel Move: 1260 High 640 NOE
Combat Move: 58 High 22 NOE
Fuel Consumption: 733.125 liters/hour (maneuver).
Fuel Capacity: 2052.75 liters LHyd plus 44.75 for fusion plant.
Endurance: 28 hours (HEPlaR), 1 month (reactor).
Armor
Config: Large Turret
Suspension: Grav
TF: 258 HF: 258
TS: 13 HS: 13
TR: 13 HR: 13
Deck: 13 Belly: 13

25mm MDAC: 600g Slug @6,000mps = 10.8Mj Kinetic Energy, with TL14
ammunition (APFSDSBSD) PV = 259. Input Energy = 17.28Mj, power source
= Pulse Fusion Cart pumping a HPC, 289 cartridges per cubic meter.
13.824 kg per cartridge (27.65 Cr each). HPG (5 chambers, ROF 1/
second) is 1.66 tons, costingMCr0.091. Total weapon system (exc/ fire
control) masses 2.506 tons and costs Cr180,000 just over a fifth of
1% of the cost of the Fusion Cradle Gun it replaces and is 1.25 tons
lighter.

Notes

This is based on the Intrepid in the RCEG, except I saw a couple of
glaring problems. Firstly, the mass and cost made it a prohibitive
weapons system to field. Since the majority of the cost was
apparently in the Fusion Cradle Gun, I replaced it. Casting around
for a replacement with similar performance but cheaper I got lucky on
my first attempt. A 2300AD inspired MDC was installed, built as
above. This saved a huge wad of cash, and was as effective a system,
using similar ammunition. Secondly, to bring down mass, I divided all
armour except the front by 10. This took 168 tons off the design,
i.e. almost 80% of the weight was taken providing this level of all
round protection. Current MBT have much stronger glacis for just this
reason, if we up armoured the whole M1A2 to the same standards as the
frontal glacis, it would weigh something like 400 tons (very rough
calculation), and be completely immobile. I left the 80 decoys in
place, although the number seems excessive, to survive 20 attacks is
unlikely at best. To survive, the Grav Tank must be smart, making pop-
up attacks, during which it's strong glacis will face the enemy. If
caught on a flank it will be destroyed, but that's a problem all
tanks (even the M1A2) face today. Research into tank point defence is
going on today, and it only seemed sensible to provide an ordnance
bay since there was over 2.5 spare cubic meters. The end result of
this process is a Grav Tank with more, not less, firepower. Sure, the
fusion gun was great, but we can buy 40 of these for 1 fusion gun
variant. The loss of armour gives the tank a lot more agility, with
an acceleration of 0.9G (loaded) rather than 0.23G, is faster and the
best defence is to avoid the hit in the first place.

 

[TheDS]

Unfortunately, my FFS1 book recently went MIA, so I can't look up the "original" corrected (erratified) stats; I had to make due with an uncorrected RCEG (which has a note to look at Ch#76 for fusion gun changes). But it looks like you killed off the armor on this thing and replaced the main fusion gun with a small Gauss gun. Right?

Tanks DO need side-armor and top-armor. And even some back- and bottom-armor. Top-attack is quite common in a futuristic battlefield, and had we been facing the cream of the Soviet crop instead of their fire-sale equipment in Iraq, I'm sure we'd've seen top-attack a much more heavily used option for our missiles' warheads.

There are other things that hunt tanks than other tanks, and you never know what direction they come from. Your design, with its pitiful side armor, would be EASY pickings to even unpowered infantry. Makes the tank fairly useless, relegating it to the likes of the Solomani combat sled, that thing that looks similar to a grav tank. Your tank could not survive even a glancing blow to the side.

Having the other faces be about half the main armor face was a good decision on the design of the original, as something with THAT MUCH armor is not vulnerable to much. Even a TL-15 Fusion Bazooka would not scratch it (much). Pretty much just stuff that's intended to hit heavy armor anyway.

OTOH, repalcing the gun with a Gauss cannon was probably a stroke of genius. That you went with such a small gun (25mm) seems at first to be a crazy idea, but it does give you a ton of high-ROF.

Using FFS2 to check your numbers tho (I'm much better with FFS1, but alas, it's not here atm, and FFS2 is usually the same thing) I think your numbers are mistaken. A 25mm round weighs considerably less than 600 grams (like, 300), and even if that's the right mass, your penetration is off. I've got 490 as the penetration for a KEAP round at TL-14, with 10.8 Mj of muzzle energy. This seems incredibly wrong to me. If I use 300g as the mass for the bullet, I get 5.4 Mj and pen 362, with a generous 7.2 Mw power requirement and ROF of 80 (per minute).

This tells me that the armor on this craft needs to be beefed up considerably (if my numbers are anything like correct). Taking a quick peek at Challenge 76, I see the revised pen for that fusion gun is a respectable 335. Considering it's a FUSION GUN and not a spitwad thrower, if my Gauss numbers are correct, then plasma STILL sucks. (I never created many gauss weapons, btw.)

Ok, so am I crazy? Is my calculator lying to me? Am I not using the rules to recreate your creation right?